Controlled molecular weight aziridine polymers

ABSTRACT

Novel branched polyalkylenepolyamine compounds having a molecular weight of from about 300 to about 3,000 are prepared by reacting an aziridine with a compound having one or more primary and/or secondary amino groups. They are useful as epoxy curing agents.

United States Patent [191 Schneider et al.

[ Sept. 25, 1973 CONTROLLED MOLECULAR WEIGHT AZIRIDINE POLYMERSInventors: James G. Schneider, Angleton;

' Clarence R. Dick; George E. Ham,

both of Lake Jackson, all of Tex.

Assignee: The Dow Chemical Company,

Midland, Mich.

Filed: Apr. 1, 1970 Appl. No.: 24,813

Related US. Application Data Continuation-impart of Ser. No. 558,555,June 20,

i 1966, Pat. No. 3,519,687.

Field of Search 260/584 R, 583 P,

References Cited UNITED STATES PATENTS Wilson 260/583 P Stoops et al260/583 P X Austin et al. 260/5705 P X Horlenko et al. 260/583 P X Riggs260/583 P X Vertnik 260/583 P Hardman 260/563 R Morgan 260/583 P XWagenaar 260/583 P X Primary ExaminerLewis Gotts AssistantExaminer-Richard L. Raymond Att0rney-Griswold and Burdick and C. E.Rehberg ABSTRACT Novel branched polyalkylenepolyamine compounds having amolecular weight of from about 300 to about 3,000 are prepared byreacting an aziridine with a compound having one or more primary and/orsecondary amino groups. They are useful as epoxy curing agents.

3 Claims, No Drawings CONTROLLED MOLECULAR WEIGHT AZIRIDINE POLYMERSCROSS-REFERENCE TO RELATED APPLICA- TlONS This is a continuation-in-partof our copending application, Ser. No. 558,555, filed June 20, 1966, nowUS. Pat. No. 3,519,687.

' BACKGROUND OF THE INVENTION The present invention relates to novelaziridine polymers having controlled molecular weights and to a processfor preparing them. More particularly, it relates to novel aziridinepolymers and a process for preparing them from an aziridine and aprimary or secondary amine, wherein the molecular weight of theaziridine polymer so prepared may be controlled by varying the moleratio of the aziridine to the primary or secondary amine.

Polymeric products prepared from an aziridine and a primary or secondaryamine are known in the art. Polymers of, for example, ethylenimine(hereinafter El) and ethylenediamine (hereinafter EDA) are disclosed inU. S. Pat. No. 2,318,729, issued May 11, 1943, and are prepared byheating EDA and El in an aqueous solution with no other catalyst thanthe water. French patent 957,308, published Feb. 16, 1950, discloses aprocess for preparing high molecular weight polymers of EDA and El whichcomprises reacting EDA and El in the presence of an acid polymerizationcatalyst. The polymers so produced have an average molecular weight ofat least 10,000.

SUMMARY OF THE INVENTION Moles aziridine Moles amine Average molecularweight:

Molecular weight) +Molecular weight of aziridine of amine The novelprocess of this invention comprises digesting, in the presence of anacid polymerization catalyst at a temperature between about and about200C. for a time sufficient to allow the resulting polymerizationreaction to go to substantial completion, a mixture of an axiridine anda primary or secondary amine in a mole ratio which will give acalculated average molecular weight according to the above formulabetween about 300 and about 3,000. The preferred temperature range isfrom about 25 to about 150C. Polymerization according to the novelprocess of this invention may be carried out in the absence of a solventor in the presence of a water solvent. To prepare novel polymers havinga minimum hydroxyl content, no water solvent is used.

The novel polymeric aziridines having a minimum hydroxyl content may berepresented by the formula:

K 112 l (R5) wherein n is an integer of from about 6 to about 70, and R,and R are, independently, hydrogen or an alkyl, aralkyl, cycloalkyl,unsaturated olefinic-, cyano-, hydroxyl-, or amine-substituted alkyl,aralkyl, or cycloalkyl group containing from 1 to about 20 carbon atoms.R and R may be bonded to form a cyclic group. However, when such acyclic group is an aziridine ring, the molecular weight of the polymerobtained cannot be predicted from the mole ratio of aziridine to primaryor secondary amine. R is hydrogen or an alkyl group of from 1 to 4carbon atoms; R is hydrogen or an alkyl, aralkyl, alkaryl, cycloalkyl,aryl, or unsaturated olefinic-, cyano-, hydroxyl-, or amine-substitutedalkyl, aralkyl, alkaryl, cycloalkyl, or aryl group containing from 1 toabout 20 carbon atoms or a branching side chain of like structure (i.e.[CH -C(R -NR H). When R is other than hydrogen, the nitrogen atom may besubstituted with both R 4 and R thus forming a quaternary nitrogen atom.R when present, is a branching side chain. Preferably, R and R in theabove formula are hydrogen, aminoethyl, hydroxyethyl, n-dodecyl, nbutyl,allyl or cyclohexyl groups, R is hydrogen or methyl, and R is hydrogen,hydroxyethyl, allyl, or phenethyl or a branching side chain. Thepolymeric aziridines of the present invention contain, in addition tothe hydroxyl groups previously defined, less than about 0.1 percent byweight hydroxyl groups when prepared under essentially anhydrousconditions. Some water, i.e. that introduced by an aqueous acid catalystsolution, may be present when the polymerization takes place.

The subject polymers are branched polyalkylenepolyamines having fromabout 5 to about 40 percent of the total nitrogen atoms in the polymeras branching sites. The degree of branching and type of branching willdepend upon the structure of the amine reactant and aziridine reactant.

Polymers prepared from El and/or C-substituted El monomers and any ofthe amine reactants are more highly branched than similar polymersprepared from N-substituted aziridines. This is due to the presence ofprimary and secondary amino groups in the polymeric product whichcompete with the amine reactant as reactive chain-initiating sites.Likewise, polymers prepared from any of the aziridine monomers and apolyamine reactant, such as ethylenediamine or diethylenetriamine, aremore highly branched than similar polymers prepared from a mono-aminereactant, such as ethylamine or diethylamine.

There are four types of branching possible in the polymers. These are(1) branching at a primary amine site(s) on the amine reactant by eachamino hydrogen being replaced with a polymer chain to give a branchedstructure, (2) branching. at two or more amine sites when the aminereactant is a polyamine, (3) branching at a secondary amine site(s) inthe polymer chain, if present, to form a tertiary amine site(s), and (4)branching at a tertiary amine site(s) in the polymer chain to form aquaternary ammonium site(s). Type (4) branching occurs when the polymersare prepared from N-substituted aziridines. The presence of such sitesis shown by nuclear magnetic resonance spectroscopy. However, aquantitative method for evaluating the degree or actual number of suchammonium groups is currently unavailable.

As a result of branching, polymers prepared from El and C-substituted EImonomers contain primary, secondary and tertiary amino groups, andpolymers prepared from N-substituted aziridine monomers contain tertiaryamino and quaternary ammonium groups and may contain primary andsecondary amino groups as terminal groups.

Suitable aziridine compounds for the process of the present inventioninclude, besides EI, both C- and N- substituted aziridines. Suitablespecific examples of C- substituted aziridines for the practice of thisinvention are disclosed, for example in Jones, The Polymerization ofOlefin Imines, in P. H. Plesch, ed. The Chemistry of CationicPolymerization, New York, MacMillan, (1963) pages 521-534. They include:2- methylethylenimine, 2-ethylethylenimine, 2,2- dimethylethylenimine,and the like. Suitable examples of N-substituted aziridines and methodsfor preparing them are disclosed by H. Bestian, Annalen 566, 210 (1950);C. A. 44 5805 (1950). They include: the N- alkyl derivatives ofethylenimine, such as N- methylethylenimine, N-ethylethylenimine, N-butylethylenimine, and the like; the N-hydroxyalkyl derivatives ofethylenimine such as N-(2-hydroxyethyl)ethylenimine, N-(Z-hydroxypropyl)ethylenimine, N-(2- hydroxybutyl)ethylenimine, and the like;ethylenimine substituted with groups containing a double bond such asN-allylethyenimine, and the like; N'substituted ethylenimines containingan aralkyl or alkaryl group, such as N-(2-phenethyl)ethylenimine;N-(Z-ethylphenyl)ethylenimine, and the like. The aziridine may alsocontain such substituents as indicated above on both the carbon andnitrogen atoms.

Suitable examples of primary and secondary amines and amines of bothprimary and secondary functionality which may be reacted with theaziridine compounds according to the process of the present inventioninclude certain aralkyl amines such as benzyl amine, phenethyl amine,and the like; aliphatic amines, such as diethyl amine, butyl amine,dibutyl amine, ethylenediamine, diethylentriamine, ethanol amine,diethanol amine, isopropanol amine, octyl amine, dioctyl amine, and thelike; cyclic amines such as morpholines, cyclohexyl amine, piperazine,and the like; miscellaneous amino compounds such as diaminodiethylether, diaminodiethylsulflde, sodium glycinate, phenyl hydrazine, lowmolecular weight polyethylenimines, e.g. those having a molecular weightbetween about 300 and 2,000, and the like. Certain of the aromaticamines, such as aniline and its derivatives, naphthylamine, and otherswherein the amine group is attached directly to an aromatic nucleus,will not give a predictable molecular weight based on the mole ratio ofamines to aziridines. Such compounds are therefore excluded from thepresent invention.

In general, any strong inorganic, organic, or Lewis acid catalyst issuitable for the process of the present invention. Examples of suitableacid catalysts include mineral acids, such as hydrochloric acid,hydrobromic acid, sulfuric acid, and the like; organic acids, such asp-toluenesulfonic acid, trichloroacetic acid, trifluoroacetic acid andthe like; strongly acidic ion-exchange resins, such as the acidicAmberlite sulfonic acid ionexchange resins sold by the Rohm and HaasCompany, the acidic Dowex 50 sulfonic acid ion-exchange resins, Lewisacids, such as aluminum trichloride, and the like.

The list of reactants and catalysts given above are intended to berepresentative rather than exclusive.

In practice, the process of the present invention is desirably carriedout by adding one of the reactants dropwise to the other over a periodof several hours, in a ratio of aziridine to amine which will give amolecular weight in the resulting product between about 300 and about3,000 as calculated by the relationship given previously. For example,to prepare a polyamine having a molecular weight of about 600 fromethylenediamine, a mole ratio of E1 to ethylenediamine of about 12.6 to1 is necessary. The mixture of reactants and acid catalyst is digestedfor a time sufficient to allow the polymerization reaction to go tosubstantial completion. The time necessary to insure completion of thepolymerization will depend on the structure of the aziridine, the amountof amines present, the temperature, the solvent, if any, and thecatalyst concentration. Times of from about 30 minutes to about hourshave been found operable.

In general, the process of the present invention is operable attemperatures within the range from about 0C. to about 200C. Attemperatures above about C., polymers prepared from N-alkyl aziridinestend to degrade in the presence of acid catalysts. The preferredtemperature range is from about 25 to 150C.

The acid polymerization catalyst is used in an amount necessary toinduce the polymerization reaction (hereinafter a catalytic amount). Forthe polymerization to be carried out within practical time limits, fromabout 0.01 percent by weight up to about 10 percent by weight as acidcatalyst of the total charge is necessary. It is preferred to keep thecatalyst concentration as low as possible and yet in a range where areasonable reaction rate is obtained. The preferred range for thecatalyst is from about 0.1 to about 5 percent by weight of the totalcharge.

The ability of the claimed process to produce polymers of molecularweight predicted from the mole ratio of aziridine to amine appears to belimited to production of polyamines having a molecular weight betweenabout 300 and about 3,000. At mole ratios of aziridine to amine suchthat the calculated molecular weight would be higher than about 3,000,the polymer is always of much lower molecular weight than predicted.

The polymers prepared by the process of the present invention are allviscous, clear liquids with an amine functionality useful for curingepoxy resin. They impart to the cured resin different propertiesdepending on the choice of amine end groups and molecular weight. Thepolymers of this invention should be particularly useful as curingagents for epoxy resins, due to the minimum hydroxyl content specifiedpreviously. They are also useful for various adhesive formulations, asintermediates for the preparation of surface active agents, and asreagents in coating compositions.

SPECIFIC EMBODIMENTS The following examples describe completelyrepresentative specific embodiments and the best modes contemplated bythe inventors for practicing the claimed invention.

The general procedure used for the examples is as follows:

Table 1 shows the results obtained by reacting a series 10 of amineswith ethylenimine (El) as the aziridine.

TABLE I EXAMPLE 2s A reaction of EDA and El is carried out with bulkmixing rather than slow addition of the El. A mixture of 156.4 g. B1,9.94 g. EDA and 1.06 g. HCl is heated at 50C. for 24 hours to effectpolymerization. After heating for two additional hours at l00C., theproduct is cooled to room temperature. The polymerization is smooth,with no appreciable exotherm, and the product is similar in appearanceand viscosity to other products made using ethylenediamine.

Polymerization of E1 with primary and secondary amines HCL Weightcatalyst,

percent of weight Obtained Calculated Plus/minus charge as Mole ratio,percent 01' Reaction Reaction molecular molecular percent Example Amineamine El/amine charge temp., C. time, hrs. weight weight deviation I1-.-. Ethylene diamine... 20. l 5. 47 0.52 85-94 6 275 295 6. 7 2.-...do 10. 1 12. 0 0. 50 81-98 6 620 600 +3. 33 3. .do 5. 24 25. 1 0.5485-95 7 1. 130 1. 140 0. 88 4- -.do 3.8 34. 4 0. 50 83-109 6. 5 1, 7051, 540 +10. 71 5- .do 2. 06 61. l 0. 50 84-120 7. 5 2, 400 2, 690 10. 786. PEI, mol. wt. 617... 46.7 16.3 0.50 67-110 1,450 1,320 +9.85 7... 034.0 28.2 0. 81-104 7.5 1,930 1,830 +5.46 8... Ethanolamine. 6. 1 22. 20.51 -96 23 914 1.015 9. 95 9... Diethanolamine..... 10. 6 20. 3 0.5160-94 22 010 080 7. 15 10 Benzylaminc 10.7 20.8 0.51 -94 22 l, 150 1,000+15. 00 11.. Allylnmlne 5. 7 22.2 0.55 60-100 35 l, 170 1,010 +15. 8212.. n-Butylamine.. 7. 25 21. i) 0. 50 05-100 23 925 1,014 8. 77 13N-dodecylamine 18.4 10. 1 0.61 65-104 26 850 1,005 -15. 41 14....Cyelohexylamin 9. 0 21. 1 0. 51 67-02 24 1. 050 1,008 +4.00

' Calculated from the relationship: Molecular weight obtained-molecularweight calculated/molecular weight calculated X100.

Table II shows the results obtained by reacting ethylenediamine (EDA)with a series of N-substituted aziridines and a C-substituted aziridine.

if only 156. 1g. of El and 1.06 g. of l-lCl are heated together at 50C.without an amine present in the mixture, the result is a violentexorthermic polymerization.

initia '11 Polymerization of substituted aziridines with EDA CatalystWeight weight percent of Mole ratio percent of Reaction ReactionObtained Calculated Plus/minus charge as aziridine/ tot temp, time,molecular molecular percent Example Auridine EDA EDA Catalyst charge Chrs. weight weight deviation 15 N-(2-hydroxyethyl)ethylenimihe. 5.9 11.2 1101 0.55 72-115 6 1,025 1,015 +0. 99 16..N-(2-phenethyl)ethylenimine. 6. 0 6. 46 HCl 0. 51 65-115 68 815 1,01010. 30 17.. o 11. 0 3. 30 E01 0. 40 100-150 4 520 545 4. 59 18.. 8. 864. 20 p-TSOH 2. 56 100-150 2 600 678 11. 51 19.. 3. 10. 2 p-IsO H n 2.702. 5 1, 550 1, 560 0. 64 20.. 3. 24 12. 2 p-TsOlI 1. 38 100 5 1, 7501,850 5. 41 21.. 5. 85 11.7 HCl 0.58 65-04 28 1, l, 030 +9.70 22Z-methylethylenimine 6. 0 16. 5 1101 0.51 73-125 46 830 1,000 17.00

-TsOII= -t0luenesullonic acid monohydrate.

b Calculate from the relationship: Molecular weight obtained-molecularweight calculated/molecular weight calculaieClXlOO.

Table 111 'sh ow sYhe results obtained from the polymerization of EDAand El when water is used as the solvent.

EXAMPLE 26 A polyeth ylenimine was prepared from El, EDA and HCl by theprocess illustrated above. The polymer was 8 Calculated from therelationship: Molecular weight obtained-molecular weightcalculated/molecular weight calculatedXlOQ.

analyzed by conventional techniques with the following results:

Analysis of polyethylenimines having average molecular weights of 600and 1800 (same method of preparation) gave essentially the same results.

EXAMPLE 27 A polymer prepared from l-(2-phenethyl) aziridine, EDA andHCl was analyzed by infrared and nuclear magnetic resonancespectroscopy. The following branching structures were indicated:

The product described in Example 7 was mixed in stoichiometric amounts(one equivalent of amine hydrogen to one equivalent of epoxy group) withthe diglycidyl ether of glycerine. A thin sheet (about 1/8 thick) of themixture was cast and cured at room temperature (about 24C.) overnight.After this time it was heated at C. for 4 hours. The resulting curedresin had a tensile strength of 3850 psi and 3 percent elongation.

EXAMPLE 29 The procedure of Example 28 was performed with the productdescribed in Example 2 and the diglycidyl ether of bisphenol A. Theresulting cured resin had a tensile strength of 7050 psi and 4 percentelongation.

The above examples show that controlled molecular weight polyamineshaving molecular weights between about 300 and 3,000 may be preparedfrom a variety of primary and secondary amines and a variety of C-substituted and N-substituted aziridines.

What is claimed is:

l. A process for preparing an aziridine polymer having an averagemolecular weight between about 300 and about 3,000 from an aziridine anda primary or secondary amine or an amine having both primary andsecondary functionality, wherein the average molecular weight of theresulting polyamine may be calculated from the mole ratio of theaziridine to primary or secondary amine present according torelationship:

Moles aziridine Molecular weight) Molecular weight of aziridine of aminesaid process comprising digesting, in aqueous solution, in the presenceof a catalytic amount of an acid polymerization catalyst, at atemperature between about 0 and about 200C, for a time sufficient toallow the resulting polymerization reaction to go to substantialcompletion, a mixture comprising an aziridine and a primary or secondaryamine in a mole ratio which will give a calculated average molecularweight according to the above relationship between about 300 and about3,000.

2. The process defined by claim 1 wherein said aziridine isethylenimine.

3. The process defined by claim 2 wherein said amine is ethylenediamine.

2. The process defined by claim 1 wherein said aziridine isethylenimine.
 3. The process defined by claim 2 wherein said amine isethylenediamine.